Ed Miliband is both wrong and right. He is wrong to assert that the NHS will be the defining issue of the next election: it will, as usual, be the economy. But he is absolutely right to choose this moment to go for the jugular on the government's health reforms. Miliband's "save the NHS" campaign coincides with a crisis of confidence on the government benches and clear signs of panic in Downing Street.

After briefings against the hapless health secretary, Andrew Lansley, from "sources" in Downing Street and three of his fellow cabinet ministers, David Cameron's belated backing lacks conviction. It's generally accepted that Lansley will be reshuffled by the autumn at the latest, but Mr Lansley's career is the least of Cameron's worries.

Today's summit on the health reforms is billed as a bid to reassure health professionals about the implementation of the changes. But even before it begins there has been a row over who is invited. Cameron is trying to divide the Royal Colleges, asking some in, while keeping harder-line rebels such as the Royal College of GPs and the British Medical Association at arm's length.

The health and social care bill is now a wreck. After the amendments ministers have had to accept, it is like a car resting on piles of bricks, its doors off and its engine in pieces. Yes, it's still theoretically a car, but it won't take you anywhere.

The government argues that it has no choice but to go ahead, since groups of GPs have already started the process of forming commissioning bodies, while the dismantling of the old trusts cannot now be reversed: in effect, "we've broken it already, so we'd better keep on breaking it". Changing course now would be difficult and embarrassing, and ragged, but Labour has offered ways of helping and bringing in the new commissioning system without legislative change and only where doctors are keen.

The problem is that the whole bill was so misconceived it cannot be coherently turned into something useful. In the service of reducing bureaucracy, it is busy creating a new, and probably eventually bigger bureaucracy. Instead of giving hospitals and GP surgeries more freedom, it is imposing a new round of top-down enforced changes on them, just at the time they are having to find big cost-savings.

In essence, what we are left with are the ambitious plans for the expansion of privately run provision, masterminded it seems by the management consultancy McKinsey, many of whose corporate clients will now bid for work inside the NHS. McKinsey is said to have earned nearly £14m from the government since the election, but this is a drop in the ocean compared with the business that private health organisations working with McKinsey now expect to gain. The extent of this one firm's involvement in shaping and directing the changes, discovered by the Mail on Sunday using Freedom of Information requests, suggests that if the "reforms" are successful, we are going to see a torrent of publicity about fat cat firms benefiting from the NHS between now and the election.

In the real world of individual NHS hospitals, if they are able to gain up to 49% of their income from private health, we will see a growing health apartheid with those who have cash or insurance policies walking up the corridors past those who haven't.

How the Liberal Democrats in the Commons can support any of this, I simply cannot imagine. Their colleagues in the Lords have been doughty, Shirley Williams above all; but Nick Clegg and Vince Cable have so far shown little spirit. Next month they will again face the wrath of party activists at their spring conference, where delegates are determined to have the issue debated. Just as they did last year, the Lib Dem grassroots are going to make clear their views on the reforms, particularly the introduction of competition, and will give more grist to the mill of the Lib Dem warriors in the Lords.

Of course there are some GPs who support the changes and there is that well-funded and vociferous private health lobby which will gain. But beyond that, this is now close to being a friendless bill. It is legislation whose political price now outweighs any positive outcome – by about tenfold.

So why is Cameron being so stubborn? Why does he declare himself "at one" with Lansley, whose attempts to explain the bill have been techno-mumble of the most desperate kind, and expend yet more political capital on a further attempt to persuade the doubters? If it were simple oldfashioned loyalty to a colleague in trouble, one might almost admire it. But nobody who knows the Tory party or this prime minister would reckon that was the real motivation.

No, it goes back to that sublime self-assurance and the way of playing Westminster politics as if it were the Eton wall game, where, however dirty you get, it's your job to push the other chap's face in the mud and keep it there. Losing the bill would give Miliband a good day. It would be "a loss". So it mustn't happen. More important to push on at all costs, and deny your opponent a moment of satisfaction. If Cameron does this, and if the Lib Dems in the Commons keep swallowing their tongues, then he probably has the votes.

It will, however, almost certainly prove a huge, longer term mistake. It will give the opposition a prime campaigning issue for the next two years. It has already alienated a big swath of health professionals. This may not matter; there aren't so many of them. But crucially, as the commercial effect of the limping legislation becomes understood, it will increasingly annoy all those people who voted for the Conservatives or the Lib Dems because they sought an end to the sense of a crony state, and instead wanted open, fair, accountable and efficient public provision.

This bill isn't that. It isn't really anything coherent. Had the coalition focused instead on more modest, measurable and practical changes, including to the running of hospitals, on shifting money towards preventative health and on the growing crisis in social care, it could have done some real good, even in tough times. But no. This has become a matter of "face" and pride. Yet we all know what comes after pride, and unless Cameron recognises that then Ed Miliband might be right after all: the NHS could become the defining issue of the next election. But for the sake of the millions who rely on the health service, let's hope he is wrong on this one.